#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a[5],i,t;
	for(i=1;i<=4;i++)
	cin>>a[i];
	for(i=1;i<=4;i++)
	{
		if(a[i]!=a[i+1]&&a[i+1]!=a[i+2])
		{
			t=i+1;
			break;
		}
		if(a[i]!=a[i+1]&&a[i]!=a[i+2])
		{
			t=i;
			break;
		}
	}
	switch(t)
	{
		case 1:cout<<"Red"; break;
		case 2:cout<<"Green"; break;
		case 3:cout<<"Blue"; break;
		case 4:cout<<"Black"; break;
	}
    return 0;
}
